PENDULAR NYSTAGMUS

Timothy C. Hain, MD • Page last modified: July 4, 2020

Pendular waveform

Pendular nystagmus refers to the waveform of an involuntary eye movement. In pendular nystagmus the eye moves in sinusoidal trajectory, similar to that of a pendulum. Pendular nystagmus generally does not have a "fast phase" including a saccade, but is composed entirely of slow eye movements. The topic of acquired pendular nystagmus was recently reviewed (Kang and Shaikh, 2017), and this page was updated to reflect content from that article. .

Pendular nystagmus is generally due to either loss of inhibitory feedback control on a neural circuit, or increased delay in a feedback circuit, that then breaks into spontaneous oscillation. This is a general characteristic of feedback control circuits with delays -- they are vulnerable to increases in gain or increased delay.

Most of the time, pendular nystagmus has a frequency of about 1 hz. This is probably because most pendular nystagmus is due to lesions in the central tegmental tract, which is part of a fairly long loop. A general principal of feedback systems is that longer loops, with longer delays, oscillate slower. If you see a faster nystagmus than 1 hz, it is likely due to a shorter feedback loop, and not part of the central tegmental tract circuitry.

Pendular nystagmus is distinguished from linear slow phase nystagmus such as is seen in vestibular disorders. It is also distinguished from most types of congenital nystagmus, where the waveform commonly has both slow and fast phases.

Mechanism of oscillations that result in pendular nystagmus.

Feedback

(from https://www.electronics-tutorials.ws/systems/negative-feedback.html)

Pendular nystagmus is a type of oscillation. Oscillations are generally caused by feedback loops. There are two general methods, a delay in a feedback loop, or a "lag" which translates into a delay that changes with frequency. When there is a net positive feedback in a loop, which can be attained in a negative feedback loop with an 180 deg phase lag, the loop can break into oscillation.

The frequency of the oscillation is set by the delay time. For example, a 1 second delay might cause an 1 hz oscillation.

While a fairly typical pendular nystagmus might have a period of 1 second, in the brain, most of the delays are much shorter than 1 sec. For example, it only takes about 200 msec response time for rather complex reactions (i.e. reaction time). Thus to create a nystagmus or tremor that has a frequency of 1 hz, a pure delay of 1 second isn't very likely.

Rather than formulating the problem in terms of neurons sending signals in a loop with a delay, there are also a physiology involved with oscillations called "gap junctions" (Juszcak et al, 2009). Gap junctions may be the mechanism for some of the pendular nystagmus that we encounter such as in oculopalatal myoclonus or in bleeds into the upper brainstem. There are many drugs that affect gap junctions, mainly relatives of quinine, that may have a role in suppressing pendular nystagmus. Little work has been done in this area.

 

Kang and Shaik (2017) provided a general discussion about the location of delays leading to pendular oscillation. One theory is that there are delays in input, such as from demyelination in visual input pathways in MS. However, aside from the situation in Congenital Nystagmus, this is generally an unlikely hypothesis as for the most part, nystagmus continues in the dark where there is no visual input. They offer a second theory that there is too much positive feedback in the brainstem neural integrator that converts velocity into position signals. We find this theory very hard to follow, and in general prefer the neural syncytium theory.

Horizontal Pendular Nystagmus

  1. Lesions of the central tegmental tract (such as due to MS)
  2. Spasmus Nutans (can also be vertical, torsional)
  3. Nystagmus of the blind
  4. Congenital nystagmus

Most frequently, horizontal pendular nystagmus is caused by central lesions involving the central tegmental tract. The concept is that there is a feedback loop that affects eye position or velocity. Lesions add delays, causing instability and nystagmus. A different version of this core idea, from the oculopalatal myoclonus literature, is that lesions of the CTT cause hypertrophy of the inferior olive, which may break into spontaneous oscillation. This seems a little more likely than the first idea.

Multiple sclerosis is the most common cause of this sort of nystagmus. Ashoff et al (1974) concluded that pendular nystagmus was caused by damage to the cerebellar nuclei, and Gresty et al (1982) suggested that the lesion was near the oculomotor nuclei. If this is true, one would think that it could oscillate more quickly than 1 hz (i.e. we are dubious). We think that the association with the cerebellum is more likely to be accurate.

Wildly uncommon inherited dysmyelinating disorders such as Pelizaeus-Merzbacher, Zellweger syndrome, and Cockayne syndrome are other examples of conditions that commonly exhibit pendular nystagmus (Kang and Shaikh, 2017; Hobson et al, 2000). However, these disorders are wildly uncommon and while most neurologists will encounter palatal myoclonus, brainstem stroke, and MS periodically, these hereditary disorders are unlikely to present outside of very rarified settings. Some discussion about these uncommon conditions that affect both horizontal and vertical circuitry is found below under elliptical nystagmus.

Gabapentin has been reported as a potential treatment for pendular nystagmus, used in doses of 600-1500 mg/day (Stahl et al, 1996). We ourselves find that gabapentin is generally useful for nystagmus of nearly any type, including congenital nystagmus, suggesting that it works on a "final common pathway". Memantine has also been reported as useful (Kang and Shaikh, 2017).

Spasmus Nutans

Spasmus nutans is a transient pendular nystagmus that occurs in children, accompanied by a head tremor and torticollus. The usual age of onset is between 4 and 18 months of age. Sometime patients with SN also have a head tremor.

The nystagmus is generally bilateral (but it can differ in each eye and may even be strictly monocular -- thus it can be dissociated -- see below), and it oscillates in horizontal, torsional, or vertical directions. An instance of spasmus nutans presenting with monocular nystagmus in monozygous twins has been reported.

Spasmus nutans may sometimes be mimicked by tumors of the optic nerve, chiasm, or third ventricle.

Pendular nystagmus of Spasmus Nutans.
Spasmus Nutans

Nystagmus of the Blind. Persons with complete blindness as well as retinal dystrophies that may preserve some vision of ten exhibit nystagmus. Follow this link for more detail.

Congenital Nystagmus (follow link). Persons with CN often combine visual issues and "wiring" problems. The wiring issue is very interesting. Follow this link to read more.

Somewhat similar to the situation with Congenital nystagmus, persons with optic gliomas combine visual issues from damage to the optic nerve and wiring issues for lesions around the optic chiasm, and commonly exhibit pendular nystagmus (Kang and Shaikh, 2017). This is probably the same situation as causes congenital nystagmus, but it is little studied.

Vertical Pendular Nystagmus

The most common cause of vertical pendular nystagmus is the vertical nystagmus that frequently appears after pontine hemorrhage. The PPRF is often damaged which makes horizontal saccades difficult, and a vertical pendular nystagmus emerges, possibly related to damage to the central tegmental tract. One wonders why MS lesions of the CTT cause mainly horizontal nystagmus, but pontine bleeds, mainly vertical nystagmus.

Treatment of vertical pendular is difficult. Herishanu and Louzoun reported a single patient who improved after chronic trihexyphenidyl treatment. The doses are relatively massive (1 mg-60 mg), precluding use in most cases because of anticholinergic side effects.

Vertical pendular nystagmus associated with oculopalatal myoclonus syndome. Recording method: infrared video

(c) 2003 Timothy C. Hain, M.D. Educational use is permitted.

Oculopalatal Myoclonus

The so-called "ocular myoclonus" associated with the oculo-palatal myoclonus syndrome, an example of which shown above, may respond to valproic acid (Lefkowitz and Harpold, 1985). It has also been reported to be successfully treated with INH (200 mg BID to QID, with pyridoxine) combined with converging prisms. In spite of these sporadic reports of success, we have not had much success ourselves. See the OPM page for more details. An extremely rare inherited disorder, Alexander's disease, also includes ocular palatal tremor (Kang and Shaikh, 2017), and presumably shares the same general pathophysiology.

Toluene Sniffing

Toluene sniffing, usually associated with glue sniffing, also can manifest as a vertical pendular nystagmus, usually in accompaniment with cognitive and cerebellar deficits (Maas et al, 1991; Kang and Shaih, 2017). Some individuals use plastic bags to inhale paint thinner (huffing). Toluene is very toxic and unfortunate individuals who "huff" also may exhibit dementia, seizures, ataxia, tremor, anosmia, ocular flutter, and numerous other results of brain damage.

 

Superior canal dehiscence.

We have seen one case of vertical pendular nystagmus due to superior canal dehiscence. Here the presumed mechanism is pulsations in CSF pressure stimulating the superior canal via the dehiscenct bone. This condition can also cause purely torsional pendular nystagmus, which is recognized by being synchronized to the pulse.

 

References re. vertical pendular nystagmus

Elliptical nystagmus

Sometimes a horizontal and vertical pendular nystagmus will occur together. They are usually of the same frequency, but their relative phase may different. Depending on the phase, the eyes may take on an oblique direction, forming a circle or an ellipse. So far, I know of no report of a nystagmus that changes relative phases (causing a pattern where the ellipse was changing). This seems possible however, as in a nystagmus called "windmill nystagmus", the vector of the horizontal nystagmus changes from right-left to up-down and back again, constantly.

Pelizaeus-Merzbacher disease (PMD), also discussed under horizontal pendular with MS, is a cause of elliptical nystagmus. It is an inherited disorder, X-linked recessive in children and autosomal dominant in adults. It affects of central white matter, with neonatal, childhood and adult onset forms. Among the leukodystrophies, PMD can be largely distinguished by its binocular pendular nystagmus and head tremor that usually begin at onset. Of the other leukodystrophies, only Cockayne's syndrome has a similar nystagmus. In Cockayne's syndrome, in addition to the findings of PMD, there are also basal ganglia calcifications. In the connatal form of PMD, death usually occurs within a few years of life. In the infantile (classical) onset form, death usually occurs in the second or third decade of life.

Torsional pendular nystagmus.

See the link above for more about torsional nystagmus.

torsional pendular

Torsion is difficult to record. One method is to have the person look to the side or up. Then torsion "cross couples" into horizontal or vertical (vertical for lateral gaze, horizontal for vertical gaze). In the recording above, an individual with high-frequency pendular was recorded looking to the side, with resulting cross coupling making it recordable.

Some patients with oculopalatal myoclonus have mainly a torsional nystagmus. We do not know why some develop vertical nystagmus and others torsional nystagmus.

Some congenital nystagmus patients have mainly a torsional pendular nystagmus. One case we encountered has no stereopsis, has a very weak torsional pendular that increases in the light compared to the dark, and seems to experience relatively little impact. In the past, he would move his head, presumably to dampen the nystagmus.

Rarely, patients with an inner ear condition (superior canal dehiscence) have a torsional pendular nystagmus. This nystagmus is synchronized with the pulse (Hain and Cherchi, 2008)

 

 

Dissociated Nystagmus (DN)

DN is a nystagmus where oscillations differ in direction or amplitude between two eyes. The eyes are "dissociated". It has been described in spasmus nutans (see above), congenital nystagmus, and various brainstem disorders, as well as disorders where there has been monocular visual loss from an early age, or acquired later in life. It also occurs when one or more of the muscles controlling an eye are weaker than on the other eye. The nystagmus is generally primarily vertical, has a pendular waveform, is of low frequency and small amplitude. We have mainly seen DN after large cerebellar strokes, typically affecting the deep cerebellar nuclei. For example, someone with a basilar artery occlusion.

A congerence/divergence nystagmus combined with contractions of the jaw muscles occurs in Whipples disease, which is an infections process in the gut. (Kang and Shaikh, 2017). Whipples is exceedingly rare, but unlike many of these other disorders, does have treatment (i.e. antibiotics).

Dissociated nystagmus is hard to record as it requires binocular cameras and high resolution. This is not a common combination in video frenzel goggle systems. So most of the time, this is probably missed.

Despite dissociation, the oscillations of the two eyes are phase locked.

Asymmetrical nystagmus can also be seen when the vergence system is involved in a nystagmus. For example, this can occur after a pontine hemorrhage. It can also occur when there is damage to oculomotor output circuitry, such in persons with brainstem hemmorages again, or specific disorders such as internuclear ophthalmoplegia, or oculomotor nuclei lesions. When this happens, both fast and slow phases are asymmetrical.

Seesaw nystagmus -- a subvariant of dissociated nystagmus.

Seesaw nystagmus is a rare binocular disorder characterized by alternating vertical skew deviation and conjugate ocular torsion. So the vertical movement is dissociated, and the torsional movement is not. Strange. Jerk seesaw consists of torsional slow phases in one direction and quick phases in the opposite. In pendular SSN, there are slow, smooth eye oscillations.

  • Rambold and others. Seesaw nystagmus associated with involuntary torsional head oscillations. Neurology 1998:51:831-837

References not already covered above: